The science of tracking millions of pieces of garbage that orbit Earth is tricky and essential.

By Stephen Ornes, 00:00 AM September 23, 2008

Each white dot represents an individual piece of tracked orbital debris. This image shows the Low Earth Orbit, which is the region from the Earth’s surface to 1,240 miles and contains the most space junk.

NASA Johnson Space Center

On a clear night, you can look in the sky and see the moon and stars. You might even see the blinking light of a working satellite as it flies past, on its way around the Earth.

And, even though you cannot see it, you are also looking at the largest junkyard in...